Compact rotary platen 3D printer

ABSTRACT

A three-dimensional printer to fabricate three dimensional objects using a rotary build surface platen. This architecture achieves high space efficiency, and rigidity for precision. The apparatus size can be very small relative to the objects it can build. The 3D printer can also actively shape the side profile of a layer for greater fidelity with the ideal input geometry. The profile can be shaped through subtraction of material, or by constraining the material while it is deposited.

FIELD

Embodiments of the invention relate to three-dimensional objectfabrication techniques. More specifically, embodiments of the inventionrelate to rapid fabrication of arbitrary three-dimensional objects.

BACKGROUND

The state of the art in fabrication of arbitrary three-dimensionalobjects is fused deposition modeling (FDM) in which tiny deposits ofplastic analogous to a pixel in a three-dimensional model are depositedindividually to build a desired object from the ground up. Among theproblems facing FDM are speed and cost. Because each subsequent depositfuses to the underlying previously deposited plastic, the size of thedeposit and the temperature control required to effect the fusing isstrictly limited. As a result, very small amounts of plastic aredeposited with each deposition and if the temperature is not preciselycontrolled, failure along corresponding knit line is manifestly likely.Moreover, because of the small amount of each deposit, the otherconstraints of controlling the system during fabrication, the timerequired to produce even a relatively simple object is measured inhours.

Among the additional problems includes the need to insure desiccation ofthe plastic supply as moisture in the supply further causes the risk offailure of proper knit during fusing. Also, because of the small amountof plastic deposited any overhang cantilevered portion of the objectmust be supported by a sacrificial material that is laid down during thefabrication process and then dissolved away post-fabrication. Thesacrificial material requirement increases the cost and time required tofabricate any particular object. Typically, both the sacrificialmaterial and the build plastic are provided as a spool often costinghundreds of dollars for a relatively small volume of plastic. Moreover,if there is insufficient plastic remaining on the spool to complete adesired build, the spool must be removed and replaced and it isdifficult to change spools mid-process or reuse a partially consumedspool. This further increases the cost associated with FDM.

A faster lower cost system with higher reliability is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention are illustrated by way of example andnot by way of limitation in the figures of the accompanying drawings inwhich like references indicate similar elements. It should be noted thatreferences to “an” embodiment of the invention in this disclosure arenot necessarily to the same embodiment, and they mean at least one.

FIG. 1 is a diagram of an external view of a fabricator of oneembodiment of the invention.

FIG. 2 is an internal view of the fabricator of one embodiment of theinvention.

FIG. 3 is a center vertical sectional view of a fabricator of oneembodiment of the invention.

FIG. 4 is a view of the melt impeller of one embodiment of theinvention.

FIG. 5 is a cross-sectional view in which the build surface andextrusion nozzle can be seen.

FIGS. 6A-C are internal views showing the addition of a sub-element to apartially constructed object.

FIG. 7 is a schematic representation of the welding process of oneembodiment of the invention.

FIG. 8 is an internal view of one embodiment of the invention with amill arm extended.

FIG. 9 is a schematic diagram of one embodiment of the invention.

FIG. 10 is a schematic diagram of an embodiment of the inventionpermitting modular expansion.

FIG. 11 is a flow diagram of operation of one embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 is a diagram of an external view of a fabricator of oneembodiment of the invention. Housing 110 has a portal 114 in its topsurface 118. Portal 114 may be accessed through sliding door 116 to loada material supply into the fabricator and also to retrieve a fabricatedobject there from. In some alternate embodiments, separate portals areprovided for loading the material supply and retrieving the fabricatedobject. In some embodiments, the portal 114 represents less than 50% ofthe area of the top surface. Interface unit 112 may provide USB ports,wireless antenna, an Ethernet port, or other suitable media ports thatfacilitate the passage into the unit of three-dimensional datarepresenting at least a portion of the geometry of a substantiallyarbitrary object to be fabricated.

FIG. 2 is an internal view of the fabricator of one embodiment of theinvention. Internally, there is an assembly zone 200 and a fabricationzone 202. Sub-elements of the ultimate three-dimensional object to becreated are fabricated within fabrication zone 202 and then put together(assembled) in assembly zone 200. To a large degree, the maximum size ofthe object to be fabricated is constrained by the size of the assemblyzone 200. To a lesser degree, the size of the fabrication zone affectsthe ultimate size of the object. In many cases, the sub-elementfabricated in fabrication zone 202 will be an entire layer of theobject. It should be understood that sub-elements may be a portion of alayer or other portion of the object consistent with the geometry thatis the source of the build instructions. It should be further understoodthat to be “consistent with the geometry”, the sub-element must have asize greater than a single voxel/pixel as a single voxel cannot bedeemed to correspond to any distinct region with the geometry.

Within assembly zone 200 resides a build platform 234 including aturntable having a build surface 208 on which the object to befabricated is assembled. Build surface 208 is provided with a rotationalaxis and a vertical axis. A driver within build platform 234 raises andlowers the build surface 208 along leadscrew shaft 232 to provide thevertical axis. An additional driver within build platform 234 rotatesbuild surface 208 so that the object being fabricated can have anyrotational orientation desired. In an alternative embodiment, the buildplatform may have x and y drives instead of a rotational drive, but suchembodiment requires a larger assembly zone for the same size object.

When build surface 208 is driven to the top of its vertical range, it isexposed through the portal (114 of FIG. 1), which permits easy access toa fabricated object.

In one embodiment, a material supply for fabrication is a monolithichelically-threaded plastic ingot 220. The helical thread acts as part ofthe drive that advances the material supply, and may be consumed andeliminated as the material is used. In alternative embodiments, thethread may be replaced with gear teeth, and index step, a flange orseries of flanges or the like, all features that may form part of thedrive system to advance the material.

Build platform 234 is driven to its maximum height to be exposed throughthe portal. Any time the build platform 234 is at its maximum height, toprotect the vertical axis from misalignment, one or more shear pinsengage the platform so that vertical or lateral forces applied by a userare not applied to the drive servo or the vertical axis. An ingot isthen loaded thereon and build platform 234 is then driven to its minimumheight along shaft 232. Plastic slide 230 then engages the plastic ingot220 from build surface 208 and transports it laterally to be accessed bythe fabrication zone 202. Extrusion collar 224 is lowered over the ingot220 and a peripheral helical ball screw drive therein engages thehelical threading of the ingot 220 to allow the extrusion collar 224 todraw the ingot 220 upward. While other ways of lifting the materialsupply are possible such as a jack type lifter etc., the collar drivereduces the vertical space requirements over those alternatives. A bentleaf spring 226 automatically engages an index slot 228 that runs thelength of the cylindrical ingot 220 to prevent the ingot 220 fromturning while the collar drive is attempting to raise it. An internaldrive 228 within the fabrication zone 202 then draws the ingot into theextrusion collar 224 so that it may provide source material for molder204.

FIG. 3 is a center vertical sectional view of a fabricator of oneembodiment of the invention. A processor 360 receives geometry for anobject to be fabricated via one or more of the interfaces (112 from FIG.1). Processor 360 then controls the drivers to control the fabricationand assembly of sub-elements described below.

As can be seen, fabrication zone 202 includes a molder 204 having acompressor 328 that receives plastic from ingot 220. Extrusion collar224 draws the ingot 220 up into contact with melt impeller 326, whichmelts and shaves the plastic and routes the resulting molten plastic viacompressor 328 to an extrusion nozzle 330. Compressor 328 provides areservoir to allow a relatively large instantaneous supply of plasticwithout requiring high pressure or rapid acceleration of the entirematerial supply. Extrusion nozzle 330 is maintained in linearrelationship with the compressor and does not translate within thefabrication zone. This linear relationship and lack of translation ofthe nozzle and supply source allows the material supply melting to occurat lower pressure, while the smaller material reservoir in thecompressor 328 can operate at high pressure and therefore draw atgreater speed. However, nozzle 330 may rotate and may be narrowed orwidened, as is discussed more fully below.

When the ingot 220 is mostly consumed, e.g., 90%, in one embodiment anew ingot can be added to follow on behind the mostly consumed ingotreducing or eliminating waste. The level of consumption required beforeaddition of an additional ingot is, to some degree, dependent on thelength of the extrusion collar as the consumed ingot should besufficiently inside the collar such that the collar can engage thehelical threading of the additional ingot. A sensor may be included tomeasure material supply usage and report the supply level via theprocessor. It is desirable to report not only a “supply low” condition,but also the volume of supply remaining so that a user can know ifsufficient material exists to complete and intended build.

Extrusion nozzle 330 is flush with a temperature-controlled plate 340and draws a desired sub-element on a temperature-controlled receivingplate 342. Plates 340 and 342 are retained in parallel relation.Receiving plate 342 may be slightly textured to allow improved grip bythe molded plastic. The slight texture or surface pitting allows theplastic molded thereon to grip or, in other words, sustain a greaterlateral force than is sustainable by plate 340. Plate 340 has a smoothsurface to allow the molded, cooled layer or sub-element to glide overthe surface and not stick thereto. For simplicity of discussion, weshall refer to sub-elements as “layers”. However, one should understandthat the discussion is equally pertinent to sub-elements generally.

By controlling the temperature of both receiving plate 342 and plate340, efficient cooling of the molded material can be assured. In oneembodiment, heat absorbed buy one or both plates in cooling the moldedplastic is recycled and returned to the melt heater via a heat pump toimprove the energy efficiency of the system.

The space 344 between plate 342 and 340 defines the thickness of thelayer. Thus, by varying the distance between the two plates, differentthickness layers of the ultimate object may be achieved. In oneembodiment, receiving plate 342 is driven by a driver to control thedistance between plates 340 and 342. The desirable thickness of a layermay depend on the variability of the edges of the object beingfabricated. For example, where the edge is uniformly vertical over adistance a thicker layer up to that distance may be used. But where theedge is very irregular thinner layers to accommodate that irregularityor slope may be desirable. Notably, the thickness of the layer is nottied to voxel dimension. As explained below with reference to FIG. 8,minor irregularities can be addressed with an integral subtractive toolexisting in some embodiments of the invention.

Additional drivers move receiving plate 342 relative to nozzle 330 topermit the arbitrary layer to be drawn. Because the aperture of nozzle330 is variable width and can rotate, thicker or thinner walls may bedrawn. In some embodiments the angular orientation or the extrusion maybe controlled by for example air jets or water jets adjacent to thenozzle 330. In other embodiments the nozzle 330 may pitch to mold anangled wall. In still other embodiments, a mechanical roller or wipermay be use to profile the side walls of the layer before or after theyhave hardened.

As with all molders, instances will occur when the molder needs to bepurged to eliminate degraded build material, etc. In one embodiment, tominimize waste and the space required for its containment, the purgedmaterial may be drawn as a disk of a desired diameter on the receivingplate 342. A waste tube having a minimally greater diameter may beprovided near the fabrication zone. The receiving plate 342 may then bedriven over to align the purge disk with the tube, lower the purge diskinto the tube and translate away, thereby scraping the purge disk offinto the tube. Subsequent purges will stack in the tube like quarters ina roll and reduce the waste storage requirements.

In one embodiment, ingot 220 formed having the helical threading alsohas a hydrophobic coating 320 which repels moisture but is also consumedas the ingot is melted. Beneath the hydrophilic coating is a core 322of, for example, ABS or other suitable thermoplastic which forms theprimary material of fabrication. Wax-based compounds may also be used asthe thermally formable material for some applications (such as lost-waxcasting mandrels). Typically the core 322 will exceed 70% by volume ofthe ingot and more commonly will exceed 95% by volume of the ingot 220.This provides a very high density of material supply in a single pieceform factor. Such an ingot is effectively self packaged reducing wasteand production costs. In some embodiments the core 322 can be formedunitarily as a whole. In other embodiments, the core 322 is formed byfirst molding a shell and then filling the shell with additionalmaterial.

Within the assembly zone, the driver 334 to drive the vertical androtational components of build surface 208 is shown. Build surface 208is part of a turntable that rotates on bearings 338 when driven bydriver 334. The turntable includes a plurality of part-off rings 336which are flush with build surface 208 during assembly. Once assembly iscomplete, rings 336 can be driven to elevate above surface 208 toseparate the fabricated object from the build surface 208. This avoids aprior art problem that the object must be split off of a build platen byhand.

FIG. 4 is a view of the melt impeller of one embodiment of theinvention. Melt impeller 326 resides within extrusion collar 224. Asextrusion collar 224 draws the plastic supply up into contact with meltimpeller 326, the melt impeller is heated to melt the surface of theplastic. Additionally, melt impeller 326 rotates and the channels 402 ofmelt impeller 326 channel the molten plastic towards the center portal406 and into the extrusion compressor. Melt impeller has a relativelylarge surface area in contact with the surface of the ingot to increasethe melting efficiency. The edges 404 of the channels 402 also serve toshave off small pieces of the plastic, further facilitating melting andallowing a relatively large volume of plastic to be delivered in a shorttime without excessive pressure.

FIG. 5 is a cross-sectional view in which the build surface andextrusion nozzle can be seen. In this view, build surface 208 andpart-off rings 336 are visible. Additionally, the surface of temperaturecontrol plate 340 and extrusion nozzle 330 are shown. Extrusion nozzle330, in this embodiment, is a slot. The length and orientation of thisslot may be varied to change the profile and orientation of the moldedplastic. In one embodiment, the slot with is under servo control as isthe rotational orientation.

FIGS. 6A-C are internal views showing the addition of a sub-element to apartially constructed product. In FIG. 6A receiving plate 342 havinglayer 604 adhered thereto translates along track drive 608 into assemblyarea 200. This clears a path for hot box 602 to shift downward to residewithin the extrusion zone below track drive 608. Hot box 602 is athermally insulated storage box with one or more ohmic heaters therein.Hot box 602 retains welding iron 620 (shown in FIGS. 6B and 6C).Receiving plate 342 then translates back over hot box 602 along trackdrive 608. The partially assembled object 606 is aligned with the layer604 by the turntable under the control of the processor as mentionedabove.

As shown in FIG. 6B, receiving plate 342 then hooks or otherwise engagesiron 620 and translates back into assembly zone 200 bringing iron 620with it. Iron 620 will be maintained at a temperature to melt thesurface of the plastic used in fabrication to a degree that permitsadhesion between two such heated layers of plastic. To that end, atemperature sensor may be coupled thereto to ensure that the ohmicheaters in the hot box 602 are engaged when the iron 620 falls below alower threshold temperature and disengaged when the iron 620 rises abovean upper threshold temperature. The iron 620 is desirably sized to beslightly larger than the largest possible object to be assembled as thisreduces the precision with which the iron must be controlled. It is alsodesirable that the iron 620 is selected to have a significant thermalmass as the ability to retain sufficient heat to conduct welds in fairlyrapid succession reduces the wattage of the ohmic heaters required toheat the iron. Typically, iron 620 will be Teflon coated or otherwisenon-stick to prevent the heated plastic from adhering thereto. It isalso desirable that the material selected for the iron 620 have a highheat transfer coefficient relative to the material to be welded. A heattransfer coefficient at least twice that of the weld constituent isdesirable and often it will be an order of magnitude or more higher.

FIG. 6C shows the iron pressed between two elements to be connected.Once receiving plate 328 has drawn iron 620 fully from the hot box, thelayer 604 is brought together with the object 606 having the iron therebetween. The pressure between the layer 604 and iron 620 causes surfacemelting on both the object 606 and the layer 604. Typically, the entireexpected contact area between the layer 604 and the expected contactsurface of the object 606. The layer 604 and object 606 are thenseparated to release the iron 620. Preferably, the iron 620 is returnedto the hot box 602 by, for example, stored mechanical force such as aspring. This results in a rapid return of the iron 620 and allows thesurface molten layer 604 and object 606 to be pressed together creatinga weld between them such that the resulting bond yields an object havingsubstantially isotropic material properties. Because such a bond isrelatively strong, it has no difficulty breaking adhesion between thereceiving plate 328 and the layer 604. Meanwhile, the hot box 602 withthe iron 620 are returned to the position above the molder as shown inFIG. 6A.

Layer 604 has now been added to the object 606 and a further layer maybe molded and added subsequently. Because a layer has its own lateralstrength, it is unnecessary to build a sacrificial layer to support it.Rather, the layers can be cantilevered or otherwise extend over a spacebelow without an underlying supporting substrate. In the case of thefirst layer, its lower surface would be melted by the iron 620 and itwould be adhered to the build surface. Once the object 606 is completed,the build platform 234 is driven to its full height to automaticallyexpose the object 606 through the portal in the top of the unit. Againat this point the shear pins engage to protect the vertical access.Then, as mentioned above, elevation of the part-off rings 336 separatesthe object 606 from the build surface. The part-off rings also help toprotect from unintentional misalignment of the vertical axis becausethey reduce lateral force that would be required if the user were tomanually break the object off the build surface.

In some embodiments, once exposed through the portal, the turntable mayrotate 360 degrees to provide a rotational display of the completedobject.

FIG. 7 is a schematic representation of the welding process of oneembodiment of the invention. At 702, the two elements to be welded arealigned. At 704, the iron is introduced between the two elements inaligned fashion. Alternatively, as previously disclosed, the alignmentand the introduction of the iron may occur concurrently. In 706, theelements are pressed against the iron to cause surface melting of bothelements. At 708, the elements are separated. At 710, the iron isremoved from between the elements. At block 712, the slightly moltensurfaces are pressed together and at stage 714 a new partial objectincluding both sub-elements then exists. In other embodiments, the probebetween the elements may introduce a glue or adhesive or additionalmolten plastic resin to cause the adhesion between the elements insteadof heating the element to melt them.

FIG. 8 is an internal view of one embodiment of the invention with amill arm extended. A mill arm 802 is shown extended to allow it todetail a partially assembled object within the assembly zone 200. Millarm 802 can typically be driven in arc to provide access to the entireobject under assembly. Mill arm 802 also includes a drive to adjust theincidence angle of the mill head 804. Typically, provided that mill head804 can reach the center of the turntable that provides build surface208, mill bit 804 can be used to detail any portion of the object simplyby appropriately rotating the build surface 208. In one embodiment, millarm is provided with a suction head to collect waste particles thatresult from the milling. In another embodiment, an air jet is providedto clear the particles from the assembly area into a collection traybelow. This avoids the risk of particles from the milling causingdefects in subsequent welds.

While layers are being added within the assembly zone, typically millarm 802 will be retracted. However, milling may be performed whileextrusion is occurring within the fabrication zone. Thus, layer-by-layeraccess to the object can be provided to mill head 804 such that portionsof the object that might be obscured when completed can be correctlydetailed during the assembly of the object. The mill is driven by themotor 806 and controlled by the internal processor (not shown). In thisway, minor defects in the extrusion fabrication may be corrected bysubtractive detailing with mill head 804. Additionally, edge detail maybe provided to permit a thicker layer to be molded than would bepossible if the extrusion needed to provide all the edge detaildirectly. Thus, the extrusion of a layer can be used to “get close” andthe mill head 804 can be use to provide added precision.

FIG. 9 is a schematic diagram of one embodiment of the invention. In oneembodiment, plural fabrication zones 902 and 904 are associated with oneassembly zone 900. Layers or sub-elements may be manufactured andassembled in an interleaved manner to improve the speed of overallfabrication. In some embodiments, a camera 910 may exist within theassembly zone. The camera may be linked to a wide area network (WAN) 914such as the Internet by link 912. Link 912 could be a wired or wirelesslink and may be direct or through a host processor. A remote node 916may the access the camera feed in substantially real time to monitor theassembly process. Remote node 916 could be a desktop computer, a smartphone, a tablet computer, a laptop, or any suitable WAN connecteddevice. Some embodiments may include cameras in the fabrication zone(s)to permit similar remote monitoring of the fabrication process inaddition to or instead of the assembly process.

Remote node 916 may also provide an interface that permits a user tosend control signals back to the fabricator to control its operation,including for example starting or stopping the process, adjustment ofsystem calibration, etc. In one embodiment, the interface is a web pageserved to the remote node 916. In some embodiments, no control panelexists on the fabricator itself and all control of the operation isperformed though the interface on remote node 916. It is also within thescope and contemplation of the invention to have plural assembly zonesin addition to plural fabrication zones. In some embodiments, one ormore layers may be assembled in a first assembly zone and then added toother layers that have been previously assembled in the second assemblyzone. By increasing the parallelism of layer production and assembly,output speeds can be increased.

FIG. 10 is a schematic diagram of an embodiment of the inventionpermitting modular expansion. An array of additive fabrication cells1002, which may be each similar to the fabrication zone described withreference to FIGS. 1-5 above, may be modularly added. In other words, auser may initially constitute the system with fewer than the 4×4 arrayof additive cells 1002 and then expand the system as demand requires to,in this example, achieve a maximum of 16 additive cells 1002. Similarly,each additive cell 1002 may have a corresponding subtractive cell 1004,such that a layer fabricated in an additive cell 1002 is transported tothe adjacent subtractive cell for detailing, for example, with a millhead, before being transported by lateral transport 1006 to elevator1008.

Elevator 1008 raises the individual platen 1010 and places it in itsintended order within the platen hopper stack 1012 residing in hopper1014. The bottom platen in the platen stack 1012 is transported intoassembly zone 1018 and aligned with build object 1016. Proper alignmentof the platens can be assured by registration holes and pins thatguarantee a known orientation. The weld layer 1020 is then welded withinthe assembly zone 1018 in a manner similar as described above inconnection with FIGS. 6A-C. Specifically, a suitable hot plate heats thesurface of both build object 1016 and weld layer 1020. The hot plate isthen removed and the layers are pressed together. In this manner,because no post-weld detailing is required, the object can be assembledlayer by layer as quickly as the welding can occur.

Once the layer is removed from its platen, the platen itself can betransported back laterally to the elevator shaft which will return it toa lateral transport 1006, which will return it to a waiting additivecell for extrusion of a subsequent layer. While in the shown embodimenta 4×4 array of additive and subtractive cells is shown, it is envisionedthat other embodiments of the invention may permit either larger orsmaller arrays of cells. Moreover, it is also envisioned that anadditional elevator hopper and assembly zone may be added, for example,to the opposite end of the fabrication array such that two objects maybe built concurrently. Notably, because the creation of layers in theadditive cells, the detailing of layers in the subtractive cells and theaddition of layers in the assembly zone can all occur in parallel,higher speed object creation is rendered possible.

In some embodiments, assembly zone 1018 is sufficient to accommodate thebuild of an object that has layers larger than any of the additive cells1002 can draw at one time. This will generally imply that edges of layersub-element should be welded together. However, by appropriatelyselecting the sub-elements of subsequent layers such that verticallypressed lamination occurs, the need for a side pressure process can beeliminated. For example, presume a cylindrical object for which anadditive cell 1002 can only produce a third of the cylinder. If thethree pieces forming each layer are shifted ten degrees on eachsubsequent layer, the weak joint between the sub-elements of any singlelayer does not cause systemic weakness in the finished object.

FIG. 11 is a flow diagram of operation of one embodiment of theinvention. At block 1102, material from which a three-dimensional objectis to be built is loaded into a fabricator. At block 1104, geometricdata corresponding to the object to be built is received in thefabricator. Geometric data may have been processed prior to loading toexpressly indicate the sub-elements in order of build, or they may beprocessed internally within the apparatus from a simplethree-dimensional model. At block 1106, a layer of the object to bebuilt is molded onto a receiving plate in a fabrication zone of theapparatus. That layer is then transported and bonded to the object beingformed at block 1108. In the case of the first layer, it is bonded to abuild surface and forms the substrate for subsequent additional layersto be bonded. A determination is made at decision block 1110 whethersubtractive detailing is required. If subtractive detailing is required,the object is milled to subtractively detail the layer at block 1112.The determination is made at block 1114 whether the object is complete.If the object is complete, the object is ejected from the fabricator atblock 1116. Otherwise, a next layer is molded and bonded and the processcontinues. It should be understood that, while this is shown as a linearflowchart, many of these operation can occur in parallel. In particular,it may be possible to mill one layer while extruding another or,depending on the number of extrusion zones and the parallelismpermitted, extruding and bonding may occur concurrently. These levels ofparallelism are intended to be within the scope and contemplation of theinvention.

While embodiments of the invention are discussed above in the context offlow diagrams reflecting a particular linear order, this is forconvenience only. In some cases, various operations may be performed ina different order than shown or various operations may occur inparallel. It should also be recognized that some operations describedwith respect to one embodiment may be advantageously incorporated intoanother embodiment. Such incorporation is expressly contemplated.

It should be appreciated that reference throughout this specification to“one embodiment” or “an embodiment” means that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the invention.

In the foregoing specification, the invention has been described withreference to the specific embodiments thereof. It will, however, beevident that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. A three-dimensional object fabrication apparatuscomprising: a structure defining a work area; an interface in thestructure to receive digital data defining a geometry for a three-dimensional object to be fabricated; a fabrication mechanism to form aportion of the object by addition of material, substantially consistentwith the digital data for a corresponding portion of the geometry; arotary table mounted within the work area such that the rotary table issubstantially fixed in at least one of an X or a Y axis relative to thehousing, the rotary table to hold the object during fabrication; and anaxis to traverse from a perimeter of a build area on the rotary table toat least a center of rotation to allow access to alter the shape of theobject.
 2. A three-dimensional object fabrication apparatus comprising:a housing enclosing a work area; an interface in the housing to receivedigital data defining a geometry for a three -dimensional object to befabricated; a fabrication mechanism to form a portion of the object byaddition of material in layers, substantially consistent with thedigital data for a corresponding portion of the geometry; wherein theside surface of a single layer is actively shaped substantiallyfollowing the corresponding portion of the geometry.
 3. The apparatus ofclaim 2 further comprising: an extrusion nozzle as part of thefabrication apparatus; and one of air jets or water jets adjacent to theextrusion nozzle to shape the side walls of a layer extruded by thenozzle.
 4. The apparatus of claim 2 further comprising: a subtractivehead to remove material from the side walls of a layer formed to changethe side profile of the layer.
 5. The apparatus of claim 2 furthercomprising: one of a wiper or a roller to change the profile of a layerwhile the layer remains in a semi solid state.
 6. The apparatus of claim1 wherein at least one external cross dimension of the housing is nomore than 1.5 times the diameter of the rotary table.
 7. The apparatusof claim 1 further comprising: a subtractive head wherein thesubtractive head includes a drive to position the head relative to theobject with at least one of a rotary platen axis, a head swing arm axis,and a head incidence angle axis.